Andrew J Taberner

University of Auckland, Окленд, Auckland, New Zealand

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Publications (96)138.81 Total impact

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    ABSTRACT: Pulse wave velocity (PWV), a measure of arterial stiffness, has been demonstrated to be an independent predictor of adverse cardiovascular outcomes. This can be derived non-invasively using cardiovascular magnetic resonance (CMR). Changes in PWV during exercise may reveal further information on vascular pathology. However, most known CMR methods for quantifying PWV are currently unsuitable for exercise stress testing. A velocity-sensitive real-time acquisition and evaluation (RACE) pulse sequence was adapted to provide interleaved acquisition of two locations in the descending aorta (at the level of the pulmonary artery bifurcation and above the renal arteries) at 7.8 ms temporal resolution. An automated method was used to calculate the foot-to-foot transit time of the velocity pulse wave. The RACE method was validated against a standard gated phase contrast (STD) method in flexible tube phantoms using a pulsatile flow pump. The method was applied in 50 healthy volunteers (28 males) aged 22–75 years using a MR-compatible cycle ergometer to achieve moderate work rate (38 ± 22 W, with a 31 ± 12 bpm increase in heart rate) in the supine position. Central pulse pressures were estimated using a MR-compatible brachial device. Scan-rescan reproducibility was evaluated in nine volunteers. Phantom PWV was 22 m/s (STD) vs. 26 ± 5 m/s (RACE) for a butyl rubber tube, and 5.5 vs. 6.1 ± 0.3 m/s for a latex rubber tube. In healthy volunteers PWV increased with age at both rest (R 2 = 0.31 p < 0.001) and exercise (R 2 = 0.40, p < 0.001). PWV was significantly increased at exercise relative to rest (0.71 ± 2.2 m/s, p = 0.04). Scan-rescan reproducibility at rest was −0.21 ± 0.68 m/s (n = 9). This study demonstrates the validity of CMR in the evaluation of PWV during exercise in healthy subjects. The results support the feasibility of using this method in evaluating of patients with systemic aortic disease.
    Full-text · Article · Dec 2015 · Journal of Cardiovascular Magnetic Resonance
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    ABSTRACT: The contraction of muscle is characterised by the development of force and movement (mechanics) together with the generation of heat (metabolism). Heat represents that component of the enthalpy of ATP hydrolysis that is not captured by the microscopic machinery of the cell for the performance of work. It arises from two conceptually and temporally distinct sources: initial metabolism and recovery metabolism. Initial metabolism comprises the hydrolysis of ATP and its rapid regeneration by hydrolysis of PCr (phosphocreatine) in the processes underlying excitation-contraction coupling and subsequent cross-bridge cycling and sliding of the contractile filaments. Recovery metabolism describes those process, both aerobic (mitochondrial) and anaerobic (cytoplasmic) that produce ATP, thereby allowing the regeneration of PCr from its hydrolysis products. An equivalent partitioning of muscle heat production is often invoked by muscle physiologists. In this formulation, total enthalpy expenditure is separated into external mechanical work (W) and heat (Q). Heat is again partitioned into three conceptually distinct components: basal, activation and force-dependent. In the following mini-Review, we trace the development of these ideas in parallel with the development of measurement techniques for separating the various thermal components.
    No preview · Article · Nov 2015 · AJP Heart and Circulatory Physiology
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    ABSTRACT: Globally millions are blind due to corneal disease, yet tissue for transplantation is a limited resource. This study characterizes the physical and biological properties of a novel collagen-based scaffold. Transparency, optical coherence tomography (OCT), and scanning electron microscopy (SEM) were used to analyse the structure of the scaffold, synthesized using rat tail collagen I. Water content was determined. The tensile strength was assessed using a micro-mechanical analyser. In vitro biocompatibility was assessed by culturing the scaffold with epithelial or keratocyte spheres. The mean scaffold transmittance was 0.72 at 358 nm, 0.88 at 570 nm, and 0.92 at 900 nm. OCT imaging confirmed that the scaffold maintained a corneal shape, with a central thickness of 502 µm and a reflectivity profile comparable to that of a normal human cornea. SEM of the scaffold revealed multiple lamellae on cross section. The mean water content was 88.7±0.7%. Ultimate tensile strength for the nonun-cross-linked scaffold was 1.23 ± 0.27 MPa compared to 2.21 ± 0.70 MPa for the cross-linked scaffold (human corneal anterior stroma 1.53 ± 0.86MPa) at a strain rate of 0.5%/s. Epithelial cells migrated over the scaffold to confluence. Keratocytes populated the scaffold and maintained a lamellar arrangement. The properties of this novel scaffold suggest that it has potential to be developed into a corneal tissue substitute for human transplantation.
    No preview · Article · Nov 2015 · Tissue Engineering Part C Methods
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    ABSTRACT: Measuring the deformation of skin in vivo is useful in a number of applications. For example, the response of skin to a variety of mechanical loadings can provide information about the health of the underlying tissue. A number of devices have been developed for measuring the surface deformation of in vivo skin. However, existing devices are typically incapable of covering large areas of skin, or are expensive. To address these issues, we present the design and evaluation of a hand-held low-cost stereoscopic device for in vivo measurement of the dynamic surface deformation of skin. A camera rig with sufficient mechanical strength was designed to hold four high-speed synchronised cameras. The field of view (FOV) of the cameras is approximately 20 mm × 20 mm. A sample 2D deformation measurement of the surface of skin was performed to show the application of this device.
    Full-text · Conference Paper · Nov 2015
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    ABSTRACT: Measuring the deformation of skin in vivo is useful in a number of applications. For example, the response of skin to a variety of mechanical loadings can provide information about the health of the underlying tissue. A number of devices have been developed for measuring the surface deformation of in vivo skin. However, existing devices are typically incapable of covering large areas of skin, or are expensive. To address these issues, we present the design and evaluation of a hand-held low-cost stereoscopic device for in vivo measurement of the dynamic surface deformation of skin. A camera rig with sufficient mechanical strength was designed to hold four high-speed synchronised cameras. The field of view (FOV) of the cameras is approximately 20 mm × 20 mm. A sample 2D deformation measurement of the surface of skin was performed to show the application of this device.
    Full-text · Conference Paper · Nov 2015
  • Rhys Williams · Bryan Ruddy · N. Hogan · Ian Hunter · Poul Nielsen · Andrew Taberner
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    ABSTRACT: Objective: A jet injector is a device that can be used to deliver liquid drugs through the skin using a fluid jet, without the use of a needle. Most jet injectors are designed and used for the delivery of inviscid liquids, and are not optimized for the delivery of viscous drug compounds. To better understand the requirements for delivering viscous drugs, we have developed a mathematical model of the electro-mechanics of a moving-coil actuated jet injector as it delivers viscous fluids. Methods: The model builds upon previous work by incorporating the nonlinear electrical properties of the motor, compliant elements of the mechanical piston and ampoule system, and the effect of viscosity on injector characteristics. The model has been validated by monitoring the movement of the piston tip and measurements of the jet force. Results: The results of the model indicate that jet speed is diminished with increasing fluid viscosity, but overshoot and ringing in the jet speed is unaffected. However, a stiffer ampoule and piston will allow for better control of the jet speed profile during an injection, and reduce ringing. Conclusion: We identified that the piston friction coefficient, the compliance of the injector components, and the viscous properties of the fluid are important determinants of performance when jet injecting viscous fluids. Significance: By expanding upon previous jet injector models, this work has provided informative simulations of jet injector characteristics and performance. The model can be used to guide the design of future jet injectors for viscous fluids.
    No preview · Article · Oct 2015 · IEEE Transactions on Biomedical Engineering

  • No preview · Article · Oct 2015 · Clinical and Experimental Ophthalmology

  • No preview · Conference Paper · Aug 2015
  • Nora C Hogan · Andrew J Taberner · Lynette A Jones · Ian W Hunter
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    ABSTRACT: Introduction: Transdermal delivery of drugs has a number of advantages in comparison to other routes of administration. The mechanical properties of skin, however, impose a barrier to administration and so most compounds are administered using hypodermic needles and syringes. In order to overcome some of the issues associated with the use of needles, a variety of non-needle devices based on jet injection technology has been developed. Areas covered: Jet injection has been used primarily for vaccine administration but has also been used to deliver macromolecules such as hormones, monoclonal antibodies and nucleic acids. A critical component in the more recent success of jet injection technology has been the active control of pressure applied to the drug during the time course of injection. Expert opinion: Jet injection systems that are electronically controllable and reversible offer significant advantages over conventional injection systems. These devices can consistently create the high pressures and jet speeds necessary to penetrate tissue and then transition smoothly to a lower jet speed for delivery of the remainder of the desired dose. It seems likely that in the future this work will result in smart drug delivery systems incorporated into personal medical devices and medical robots for in-home disease management and healthcare.
    No preview · Article · May 2015 · Expert Opinion on Drug Delivery
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    ABSTRACT: Isolated ventricular trabeculae are the most common experimental preparations used in the study of cardiac energetics. However, the experiments have been conducted at sub-physiological temperatures. We have overcome this limitation by designing and constructing a novel calorimeter with sufficiently high thermal resolution for simultaneously measuring the heat output and force production of isolated, contracting, ventricular trabeculae at body temperature. This development was largely motivated by the need to better understand cardiac energetics by performing such measurements at body temperature to relate tissue performance to whole heart behavior in vivo. Our approach uses solid-state thermoelectric modules, tailored for both temperature sensing and temperature control. The thermoelectric modules have high sensitivity and low noise which, when coupled with a multi-level temperature control system, enable an exceptionally high temperature resolution with a noise-equivalent power an order of magnitude greater than those of other existing muscle calorimeters. Our system allows us to rapidly and easily change the experimental temperature without disturbing the state of the muscle. Our calorimeter is useful in many experiments that explore the energetics of normal physiology as well as pathophysiology of cardiac muscle. Copyright © 2015, American Journal of Physiology - Heart and Circulatory Physiology.
    No preview · Article · May 2015 · AJP Heart and Circulatory Physiology
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    ABSTRACT: Elevated systemic blood pressure, and the attendant development of pathologic left ventricular (LV) hypertrophy, ultimately culminates in heart failure and death. In clinical studies, a reduction of myocardial efficiency has been implicated in systemic hypertensive-hypertrophy. However, it is uncertain whether reduced efficiency correlates with LV wall thickness. Hence, we performed experiments on isolated working hearts of spontaneously hypertensive rats (SHRs)-a widely-used experimental model of human hypertensive-hypertrophy. We contrasted their mechanoenergetic performance with that of Wistar controls at two ages: Adult (9 months) and Aged (post-18 months). The use of animal hearts allowed us to perform experiments over a wide range of afterloads. We found that mechanoenergetic performance (coronary and aortic flows, work output and oxygen consumption) declined with age. The peak efficiency of the Adult SHR was essentially similar to that of Control, but that for the Aged SHR was lower, compared with that of age-matched Wistar rats. All variables, including peak efficiency, obtained from the failing Aged SHR hearts (which also developed right ventricular hypertrophy), were greatly reduced. Our data reveal that peak efficiency of the Aged SHR, upon transitioning from compensated hypertrophy to failure, diminishes sharply, arising from compromised flows-both aortic and coronary. We further show that the reduction of myocardial efficiency in hypertensive-hypertrophy does not correlate with LV wall thickness, but instead is inversely correlated with whole-heart mass. The latter relation may serve as a prognostic and diagnostic tool in the clinical setting.Hypertension Research advance online publication, 19 March 2015; doi:10.1038/hr.2015.37.
    No preview · Article · Mar 2015 · Hypertension Research
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    ABSTRACT: Design and develop an automated, hand-held instrument (elastometer) to assess in vivo passive stiffness of the pelvic floor muscle. The elastometer system consisted of a hand piece, real-time controller, and laptop computer. A cable connected the hand-piece to the controller, which communicated with a laptop computer via an ethernet connection. Force sensitivity calibration and displacement accuracy were determined experimentally using a spring load and an Instron mechanical tester. A test re-test series quantified the in vivo repeatability (within a procedure) and reproducibility (between procedures after a 5 min delay) of passive stiffness in volunteers (n = 20). Stiffness was determined from the gradient of the force-displacement curve for each cycle. The force-aperture spring measurements from the elastometer showed consistent (r(2) = 1.0000) agreement with those measured by the Instron. The difference between spring stiffness as measured by the elastometer and the Instron (388.1 N/m cf. 388.5 N/m, respectively) was negligible. The intra-class correlation coefficient for repeatability within procedures was 0.986 95% CI (0.964-0.994) n = 20, and reproducibility between procedures ICC 0.934 (95% CI 0.779-0.981) n = 12. Bland-Altman analysis determined a bias of 0.3 and 18.5 N/m, for repeatability and reproducibility respectively. Neither bias is likely to be clinically significance. The elastometer demonstrated very good repeatability and accuracy in the measurement of force/displacement during in vitro testing. There was a high degree of repeatability and reproducibility in stiffness measurements in a test re-test series. Our results demonstrate the elastometer is accurate and reliable and thereby suitable for larger clinical trials. Neurourol. Urodynam. © 2013 Wiley Periodicals, Inc.
    Full-text · Article · Feb 2015 · Neurourology and Urodynamics

  • No preview · Article · Jan 2015 · Biophysical Journal
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    Cormac Flynn · Andrew J Taberner · Sidney Fels · Poul M F Nielsen

    Full-text · Conference Paper · Nov 2014
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    ABSTRACT: Long-term systemic arterial hypertension, and its associated compensatory response of left-ventricular hypertrophy, is fatal. This disease leads to cardiac failure and culminates in death. The spontaneously hypertensive rat (SHR) is an excellent animal model for studying this pathology, suffering from ventricular failure beginning at about 18 months of age. In this study, we isolated left-ventricular trabeculae from SHR-F hearts and contrasted their mechanoenergetic performance with those from nonfailing SHR (SHR-NF) and normotensive Wistar rats. Our results show that, whereas the performance of the SHR-F differed little from that of the SHR-NF, both SHR groups performed less stress-length work than that of Wistar trabeculae. Their lower work output arose from reduced ability to produce sufficient force and shortening. Neither their heat production nor their enthalpy output (the sum of work and heat), particularly the energy cost of Ca2+ cycling, differed from that of the Wistar controls. Consequently, mechanical efficiency (the ratio of work to change of enthalpy) of both SHR groups was lower than that of the Wistar trabeculae. Our data suggest that in hypertension-induced left-ventricular hypertrophy, the mechanical performance of the tissue is compromised such that myocardial efficiency is reduced.
    Full-text · Article · Nov 2014
  • Ho Yan Leung · David M Budgett · Andrew Taberner · Patrick Hu
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    ABSTRACT: Determining heat losses in power transfer components operating at high frequencies for implantable inductive power transfer systems is important for assessing whether the heat dissipated by the component is acceptable for implantation and medical use. However, this is a challenge at high frequencies and voltages due to limitations in electronic instrumentation. Calorimetric methods of power measurement are immune to the effects of high frequencies and voltages; hence, the measurement is independent of the electrical characteristics of the system. Calorimeters have been widely used to measure the losses of high power electrical components (>50 W), however it is more difficult to perform on low power components. This paper presents a novel power measurement method for components dissipating anywhere between 0.2 W and 1 W of power based on a heat balance calorimeter that uses a Peltier device as a balance sensor. The proposed balance calorimeter has a single test accuracy of ±0.042 W. The experimental results revealed that there was up to 35% difference between the power measurements obtained with electrical methods and the proposed calorimeter.
    No preview · Article · Aug 2014 · Measurement Science and Technology
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    ABSTRACT: An integrated instrument is being developed to study live cardiac trabeculae, which is capable of stimulating the muscle under controlled conditions while measuring the heat production, force, and sarcomere length distribution. To improve the accuracy of estimation of stress, strain, and volumetric heat production, the geometry of the muscle must be known. A spectral domain optical coherence tomography system (SD-OCT) has been constructed and calibrated to image the trabecula mounted inside the instrument. This system was mounted above the muscle chamber and a series of equally-spaced cross-sectional images were obtained. These were processed using a workflow developed to extract cross-sectional area and volume. The initial results have demonstrated the feasibility of using OCT to capture the overall geometry of cardiac trabecula mounted in the instrument. Further work will be directed to improve the image quality for larger samples and apply meshing algorithms to the acquired data.
    Full-text · Article · Aug 2014
  • Bryan P Ruddy · Ian W Hunter · Andrew J Taberner
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    ABSTRACT: We present a scaling model for electrically-actuated needle free jet injectors, establishing the relationship between injection volume and motor size. Using an analytical electromagnetic model for the motor, we derive an optimal motor design, and show that this design is approximately scale-invariant. To illustrate the utility of this model, we then describe the design of a motor for use with 300μL disposable injection ampoules with a mass of just 300g, including a light-weight support structure. Experimental verification of the motor performance shows close agreement to model predictions, with a peak force of 1000 N/kg and a 150 m/s water jet delivered.
    No preview · Article · Aug 2014
  • Adam M Reeve · Martyn P Nash · Andrew J Taberner · Poul M F Nielsen
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    ABSTRACT: Vascularized biological tissue has been shown to increase in stiffness with increased perfusion pressure. The interaction between blood in the vasculature and other tissue components can be modeled with a poroelastic, biphasic approach. The ability of this model to reproduce the pressure-driven stiffening behavior exhibited by some tissues depends on the choice of the mechanical constitutive relation, defined by the Helmholtz free energy density of the skeleton. We analyzed the behavior of a number of isotropic poroelastic constitutive relations by applying a swelling pressure, followed by homogeneous uniaxial or simple-shear deformation. Our results demonstrate that a strain-stiffening constitutive relation is required for a material to show pressure-driven stiffening, and that the strain-stiffening terms must be volume-dependent.
    No preview · Article · May 2014 · Journal of Biomechanical Engineering
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    ABSTRACT: Diabetes induces numerous electrical, ionic and biochemical defects in the heart. A general feature of diabetic myocardium is its low rate of activity, commonly characterised by prolonged twitch duration. This diabetes-induced mechanical change, however, seems to have no effect on contractile performance (i.e., force production) at the tissue level. Hence, we hypothesise that diabetes has no effect on either myocardial work output or heat production and, consequently, the dependence of myocardial efficiency on afterload of diabetic tissue is the same as that of healthy tissue. We used isolated left ventricular trabeculae (streptozotocin-induced diabetes versus control) as our experimental tissue preparations. We measured a number of indices of mechanical (stress production, twitch duration, extent of shortening, shortening velocity, shortening power, stiffness, and work output) and energetic (heat production, change of enthalpy, and efficiency) performance. We calculated efficiency as the ratio of work output to change of enthalpy (the sum of work and heat). Consistent with literature results, we showed that peak twitch stress of diabetic tissue was normal despite suffering prolonged duration. We report, for the first time, the effect of diabetes on mechanoenergetic performance. We found that the indices of performance listed above were unaffected by diabetes. Hence, since neither work output nor change of enthalpy was affected, the efficiency-afterload relation of diabetic tissue was unaffected, as hypothesised. Diabetes prolongs twitch duration without having an effect on work output or heat production, and hence efficiency, of isolated ventricular trabeculae. Collectively, our results, arising from isolated trabeculae, reconcile the discrepancy between the mechanical performance of the whole heart and its tissues.
    Full-text · Article · Apr 2014 · Cardiovascular Diabetology